1. Field of the Invention
The present invention relates to an image recording apparatus capable of performing image recording using a plurality of colors.
2. Description of the Related Art
In a conventional image recording apparatus for recording a plurality of color images, a color space (to be referred to as an "input color space" hereinafter) used upon designation of image colors does not always coincide with a color space (to be referred to as an "output color space" hereinafter) for actually recording an image.
In many apparatuses, the two color spaces do not coincide with each other such that the input color space used upon designation of image colors is a color space of red, green, and blue (RGB color space; a reference light source is a C light source of the CIE) of the NTSC standards, and the output color space used in actual image recording is a color space of yellow, magenta, cyan, and black (YMCK color space) inherent to a recording apparatus.
For this reason, in the image recording apparatus, the values in the output color space must be obtained by converting the designated values in the input color space so as to reproduce colors designated in the input color space.
Conversion from the values in the input color space to the values in the output color space will be referred to as color processing hereinafter.
Various color processing methods have been proposed and put into practical applications.
FIG. 4 shows an example of conventional color processing.
In the example shown in FIG. 4, the input color space is an RGB color space of the NTSC standards, and is converted into a YMCK color space inherent to the recording apparatus.
A LOG converter 41 performs conversion using a logarithmic function, and a masking circuit 42 then performs linear conversion based on the values converted by the LOG converter 41. The linear conversion results are determined as the values in the YMCK color space. The conversion coefficient values used in the linear conversion in the masking circuit 42 are determined in consideration of ink characteristics, and the like of a recording apparatus of interest. FIG. 4 also shows masking formulas used in the conversion of the conventional masking circuit.
As described above, the conventional image recording apparatus for recording an image having a plurality of colors converts colors designated in the input color space into values in the output color space, thereafter, generates patterns in units of output colors, and then performs recording.
For this reason, a numerical value calculation amount in the color processing for reproducing the colors designated in the input color space is large, and a processing time required for this calculation prolongs a time required for image recording.
In some prior arts, the color processing is simplified to decrease a calculation amount so as to shorten the color processing time. However, the colors of a recorded image considerably become different from the designated colors.